Universal joints, and especially constant velocity joints, operate to transmit torque between two rotational members. The rotational members are typically interconnected by a cage, or yoke, that allows the rotational members to operate with their respective axes at a relative angle. Constant velocity joints and similar rotating couplings typically include a boot cover assembly and grease cover to enclose and protect the coupling during operation. Since the boot cover assembly is partially flexible, the boot cover assembly is able to seal around the joint while permitting articulation and relative axial movement of differing rotating members of the joint. The boot cover assembly and the grease cover seal lubricant in the joint so as to reduce friction and extend the life of the joint. The boot cover assembly and the grease cover also seal out dirt, water and other contaminants to protect the functionality of the joint. However, leaks may reduce the life of the joint, and contaminants in the grease may disturb the chemical composition of the grease, degrading its performance.
Universal joints are commonly classified by their operating characteristics. One important operating characteristic relates to the relative angular velocities of the two shafts connected thereby. In a constant velocity type of universal joint, the instantaneous angular velocities of the two shafts are always equal, regardless of the relative angular orientation between the two shafts. In a non-constant velocity type of universal joint, the instantaneous angular velocities of the two shafts vary with the angular orientation (although the average angular velocities for a complete rotation are equal as one shaft accelerates and decelerates relative to the rotational speed of the other shaft, creating a rotational speed oscillation). Another important operating characteristic of a joint may be the ability of the joint to allow relative axial movement between the two shafts. A fixed joint does not allow this relative movement, while a plunge joint does.
FIG. 1 illustrates an exemplary the CVJ 20. The CVJ 20 includes driven end 22 and a driving end 24. The CVJ 20 further includes a joint assembly 26 coupled to a shaft 28 with a boot cover assembly 30 connected therebetween. The CVJ 20 further includes a grease cover 32 that seals the driven end 22. The boot cover assembly 30 includes a metal cover 34 and a flexible boot 40. A portion of the metal cover 34 is crimped onto the boot 40 for attachment thereto. The boot cover assembly 30 protects the moving parts of the CVJ 20 during operation. The joint assembly 26 includes a first rotational member 42, a second rotational member 44, and a plurality of balls 46 retained in a race 48. The shaft 28 is splined to the second rotational member 44 to allow axial movement therebetween.
When the instantaneous angular velocities of two portions of a driveline are not equal, the differences in velocities will impart a torsional oscillation into the driveline. That is, for example, since the instantaneous rotational velocity of at least the balls 46 and the race 48 are different than the instantaneous rotational velocity of the first rotational member 42 and the second rotational member 44 when the joint 20 is operating at an angle (the first rotational member 42 and the second rotational member 44 are not coaxial), torque and rotational velocity that is transmitted from the first rotational member 42 to the second rotational member 44 will include an oscillatory magnitude imparted by a fraction of the rotational inertia of the balls 46 and the race 48. A rotational speed or torque with an oscillatory magnitude may undesirably drive other vibrations within a drive train or a vehicle, or may reduce the useful life of drivetrain components.
Other contributors of oscillatory magnitude of rotational speed and torque within a drivetrain include the combustion events in an internal combustion engine, gear backlash, and the magnetic field pull and push between the magnet and the armature of an electric motor. While a large portion of the magnitude of these oscillations may be dampened by the torsional deflection of torque transmitting shafts and torsional dampers, such as those found in clutch disks, some oscillatory magnitude will typically transmit through the driveline. Additionally, shorter shafts may result in less ‘absorption’ of rotational speed and torque oscillations, resulting in a greater magnitude of transmitted oscillations.
What is needed, therefore, is an apparatus and method of reducing or eliminating the oscillatory magnitude of rotational speed and torque within a drivetrain.